Light emitting diode selection circuit

Abstract

The present invention relates to a Light Emitting Diode (LED) selection circuit for an LED driver that drives multiple unequal lengths of LED strings, which selectively turns the LED strings ON and OFF corresponding to an input alternating current (AC) line voltage. The LED driver provides optimal efficiency as input AC line voltage varies from low to high voltages (i.e. 90V to 150V for nominal 120 VAC operation and 190V to 250V for nominal 220 VAC operation). Thus The LED driver can be used internationally since it accepts voltages from virtually every industrialized country in the world. The LED selection circuit in accordance with the present invention comprises a rectifier, multiple LED strings, multiple current sources and a controller. The controller generates multiple signals to the corresponding current source and turns ON and OFF the LED strings.

1. A Light Emitting Diode (LED) selection circuit comprising:
 a rectifier converting an input Alternating Current (AC) line voltage to a pulsating Direct Current (DC) voltage; 
 multiple LED strings; 
 multiple current sources, each current source comprising
 an error amplifier having a first input end, a second input end and an output end; and 
 a transistor having a drain, a source and a gate, the drain of the transistor being connected to a bottom side of the corresponding LED string, the source of the transistor being connected to the second input end of the error amplifier and one end of a current sensing resistor, the gate of the transistor being connected to the output end of the error amplifier, wherein another end of the current sensing resistor is connected to the rectifier; and 
 a controller being connected to the rectifier and the current sources and turning ON and OFF the corresponding LED strings, wherein the controller synchronizes frequencies of the pulsating DC voltage and generates multiple reference voltages to the corresponding current sources at an appropriate time. 
 
 
     
     
       2. The LED selection circuit as claimed in claim wherein the controller turns OFF the current in the LED string at least one time during a half wave cycle so that the LED brightness modulation frequency being higher than twice the AC input line voltage. 
     
     
       3. The LED selection circuit as claimed in  claim 1 , further comprising
 at least one dividing current source dividing each of the LED strings into multiple segments respectively, and comprising
 the first dividing current source being connected to the LED string and the current source, and the LED string being divided to a first segment and a second segment; and 
 the second dividing current source being connected to the LED string, the first dividing current source and the current source, and the LED string being divided into a third segment; and 
 
 wherein the reference voltage provided by the controller comprises multiple preset voltages indicative of a specific current level respectively to the first dividing current source, the second dividing current source and the current source, which the preset voltage provided to the first dividing current source is lower than the preset voltage provided to the second dividing current source, the preset voltage provided to the second dividing current source is lower than the preset voltage provided to the current source. 
 
     
     
       4. The LED selection circuit as claimed in  claim 3 , wherein
 the first dividing current source comprises
 a first dividing error amplifier comprising a first input end, a second input end and an output end; and 
 a first transistor comprising
 a drain being connected to the first segment; 
 a source being connected to the second input end of the first error amplifier; and 
 a gate being connected to the output end of the first error amplifier; and 
 
 
 the second dividing current source comprises
 a second dividing error amplifier comprising a first input end, a second input end and an output end; and 
 a second transistor comprising
 a drain being connected to the second segment; 
 a gate being connected to the output end of the second error amplifier; and a source being connected to the second input end of the second error amplifier, the first dividing current source and the current sensing resistor. 
 
 
 
     
     
       5. An LED selection circuit, for switching between 120 Volts, Alternating Current (VAC) and 240 VAC operation of an LED driver, comprising
 a rectifier converting an input AC line voltage to a pulsating DC voltage; 
 multiple LED strings comprising a first LED string and a second LED string; 
 multiple current sources, each current source comprising
 an error amplifier having a first input end, a second input end and an output end; and 
 a transistor having a drain, a source and a gate, the drain of the transistor being connected to a bottom side of the corresponding LED string, the source of the transistor being connected to the second input end of the error amplifier and a current sensing resistor, the gate of the transistor being connected to the output end of the error amplifier; 
 a high voltage (HV) diode being coupled between the first LED string and the second LED string, wherein an anode of the HV diode is connected to the first LED string; 
 a PMOS module being connected to the rectifier, the second LED string and a cathode of the HV diode; 
 a peak sensing module being connected to the rectifier and sensing peak information of the pulsating DC voltage; 
 a second NMOS transistor; and 
 a controller receiving the peak information from the peak sensing module, and turning the second NMOS transistor to configure the first LED string and the second LED string being connected in parallel or in series. 
 
 
     
     
       6. The LED selection circuit as claimed in  claim 5 , further comprising a first NMOS transistor and an inverter is connected between gates of the first NMOS transistor and the second NMOS transistor, the drains of the first the second NMOS transistor are connected to the PMOS module and the sources are tied to a common ground. 
     
     
       7. The LED selection circuit as claimed in  claim 5 , wherein the controller turns the second NMOS transistor ON when the input AC line voltage is in 120 VAC voltage range, the PMOS module causes the HV diode to block current flow from the first LED string to the second LED string, and thus the first LED string and the second LED string are configured in parallel. 
     
     
       8. The LED selection circuit as claimed in  claim 5 , wherein the controller turns the second NMOS transistor OFF when the input AC line voltage is in 240 VAC voltage range, the PMOS module allows the HV diode to become forward biased and configures first LED string and the second LED string in series. 
     
     
       9. An LED selection circuit, for switching between 120 VAC and 240 VAC operation of an LED driver, comprising
 a rectifier converting an input AC line voltage to a pulsating DC voltage; 
 multiple LED strings comprising a first LED string and a second LED string, wherein the first LED string and the second LED string are connected in series as default; 
 multiple current sources, each current source comprising
 an error amplifier having a first input end, a second input end and an output end; and 
 a transistor having a drain, a source and a gate, the drain of the transistor being connected to a bottom side of the corresponding LED string, the source of the transistor being connected to the second input end of the error amplifier, the gate of the transistor being connected to the output end of the error amplifier; 
 a high voltage (HV) diode being coupled between the first LED string and the second LED string, wherein an anode of the HV diode is connected to the first LED; 
 a NMOS module comprising
 a switching component; 
 a third NMOS transistor comprising
 a gate being coupled to the switching component; 
 a source being connected to a cathode end of the HV diode; and 
 a drain being connected to the rectifier; and 
 
 a capacitor; 
 a blocking diode; 
 a resistor, the capacitor and the resistor are parallel connected between the gate and the source of the third NMOS transistor; 
 a voltage source being coupled to the gate of the third NMOS transistor through the switching component and the blocking diode; and 
 a fourth NMOS transistor comprising
 a gate being coupled to the controller; and 
 a drain being connected to the source of the third NMOS transistor; and 
 
 
 
 a controller determining current through a first feedback resistor, and turning the third NMOS transistor and the fourth NMOS transistor to configure the first LED string and the second LED string being connected in parallel or in series. 
 
     
     
       10. The LED selection circuit as claimed in  claim 9 , further comprising
 a second feedback resistor; 
 a first dividing module being connected to the first LED string and dividing the first LED string to a first segment and a second segment; 
 a second dividing module being connected to the second LED string and dividing the second LED string to a third segment and a fourth segment; and 
 wherein, the first current dividing module uses a feedback voltage from the second feedback resistor in parallel operation, and uses the sum of a feedback voltage across the first feedback resistor and the second feedback resistor in series operation. 
 
     
     
       11. The LED selection circuit as claimed in  claim 10 , wherein
 the first dividing module comprises
 a first dividing current source receiving a first preset voltage level indicative of a current in the current source and being connected between the first segment and the second segment of the first LED string; and 
 a second dividing current source receiving a second preset voltage level indicative of a current in the current source and being connected between the second segment and the anode of the HV diode; and 
 
 the second dividing module comprises
 a third dividing current source receiving a third preset voltage level indicative of a current in the current source and being connected between the third segment and the fourth segment of the second LED string; and 
 a fourth dividing current source receiving a fourth preset voltage level indicative of a current in the current source and being connected to the fourth segment of the second LED string and the first feedback resistor.